The overall goal of the proposed experiments is to elucidate the molecular and cellular mechanisms underlying selective vulnerability of particular brain cell populations in thiamine deficiency and to ascertain how age and genetics (i.e. strain) modify the response to thiamine deficiency. Thiamine deficiency in man and animals produces a delirium or metabolic encephalopathy - including diminished brain function and selective cell death. Furthermore, thiamine pyrophosphate dependent enzymes are dramatically reduced in autopsied brains from Alzheimer patients. Our previous results demonstrate that thiamine deficiency reduces the activity of thiamine pyrophosphate dependent enzymes in whole brain and in small regions of free hand dissected tissues; however, even the smallest pieces of tissue may contain both affected and unaffected cells. The availability of the appropriate antibodies, which allow these enzymes to be assessed at the cellular level, and the surprising observation, that oxidative enzymes show cell and region specific distribution, suggest the following approaches. The initial studies will examine, by immunocytochemistry, the cell type and region specific distribution of thiamine pyrophosphate dependent enzymes in mouse brain and determine if thiamine deficiency produces selective reductions in these variables. Since oxidative metabolism and calcium regulation are closely linked, changes in these enzymes during thiamine deficiency will be compared to in vivo and in vitro measures of calcium homeostasis. Whether thiamine-deficiency induced changes in calcium and thiamine pyrophosphate dependent enzymes are related to selective cell death will be assessed. In our previous studies with a rodent model of thiamine deficiency, both genetics (i.e. strain) and age modify the behavioral and biochemical response. Thus, whether the thiamine pyrophosphate dependent enzymes, altered calcium homeostasis or selective cell death underlie the predisposing effects of age and strain on the response to thiamine deficiency will be examined. The results will lay the foundation for future studies that will allow us to examine the relation of these changes to particular neurotransmitter systems and to gene expression at molecular and cellular levels. The results of the proposed studies will help to elucidate why these thiamine pyrophosphate dependent enzymes are dramatically reduced in Alzheimer's disease.